Tungsten/powdered metal/polymer high density non-toxic composites

ABSTRACT

Tungsten/polymer composites comprising tungsten powder, another metal powder having a high packing density, and organic binder have high density, good processibility and good malleability. Such composites are useful as lead replacements, particularly in the manufacture of shot.

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims the benefit of U.S. ProvisionalApplication No. 60/329,307 filed Oct. 16, 2001.

FIELD OF THE INVENTION

[0002] This invention relates to composite materials, particularly tocomposite materials that can be used as lead replacements.

BACKGROUND OF THE INVENTION

[0003] Lead has been used in a variety of industrial applications formany thousands of years. In the last hundred years, the toxic effects oflead ingestion on humans, and wildlife in general, have become apparent.Throughout the world various environmental agencies classify the metaland many lead compounds, including oxides, as Hazardous Wastes.

[0004] As an example, in the USA, about 51% of lead solid waste, has inthe past, been due to spent ammunition and ordinance. Lead shot used forhunting waterfowl is now prohibited because of its toxicity to birdsthat are wounded but not killed and to wildlife that ingest loose shot.Firing of small arms ammunition for training, sporting, law enforcementand military purposes contributes a significant potential forenvironmental pollution and constitutes a human health risk. In the USAthe Department of Energy, (DOE), expends about 10 million rounds ofsmall arms ammunition each year, resulting in a deposit of over 100tonnes of lead. The DOE's use of ammunition is small compared with thatof civilians, law enforcement agencies and the Department of Defence.Overall, it is estimated that in the USA, hundreds of tonnes of lead arereleased into the environment every day.

[0005] By way of a further example, lead is commonly used to balanceautomobile wheels. Wheel balancing weights are applied to wheel rims tocompensate for static and dynamic unbalances and guarantee true runningof the tyres. The European End of Life Vehicle (ELV) Directive aims atreducing the use of hazardous materials and states in Article 2.2(a):

[0006] Member States shall ensure that materials and components ofvehicles put on the market after Jul. 1, 2003 do not contain lead,mercury, cadmium or hexavalent chromium other than in cases listed inAnnex II under the conditions specified therein [emphasis added].

[0007] Between 1991-1992 a study was carried out in Houston, USA, by theHouston Advanced Research Centre, (HARC in which weights had beencollected from the roadside, having been lost from vehicles. Hundreds oflead weights weighing 26 kg had been collected from a four-mile stretchof road over 9 months.

[0008] In a 1999 letter to the Electronics Engineering Times, anindividual in the US reported casually finding about 2.5 kg of leadweights on a short stretch of busy road in just 1 day. A more detailedstudy was carried out in Albuquerque, N. Mex., USA, and published byRoot. This showed that very large quantities of lead weights were lostfrom vehicles—approximately 8 kg/km/year for a large urban highwayrising to between 50 and 70 kg/km/year at one intersection. A total of3.7 tonnes per year was estimated for the major Albuquerquethoroughfares.

[0009] The total quantity of weights deposited on the roads of the UKand Europe cannot be estimated accurately but is possibly of the orderof 1,500 tonnes per year, representing a loss of around 1 in 10 fittedweights.

[0010] Alternative materials for weights evaluated so far are tin,steel, zinc, tungsten, plastic (thermoplastic PP) and ZAMA, which is analloy of ZnAl4Cu1. All these materials apart from tungsten havedensities far below that of lead and do not have the ideal combinationof mechanical and physiochemical properties.

[0011] In an effort to reduce reliance on lead in many applications,there has recently been extensive research into materials that could beused to replace it.

[0012] In this regard, much effort has been focused on producing metalcomposites that mimic the properties of lead. Since the density of leadis the most obvious characteristic to mimic, most efforts haveconcentrated on finding composites that have the same or similardensity. However, other important properties of lead have been largelyignored and, as a result, no completely satisfactory lead replacementhas yet been found.

[0013] In addition to the requirement of being non-toxic and to having asimilar density to lead, a successful composite should have reasonableformability coupled with structural rigidity. For many of the leadreplacement applications envisaged, the composite should ideally besubstantially homogeneous and relatively low cost to manufacture inlarge quantities.

[0014] Tungsten-polymer composites have been used as lead-free systemsfor various applications. A practical limitation of these systems isthat the packing characteristics of commercial tungsten powders aretypically poor owing to their non-spherical shape and typicallyagglomerated state. The inferior packing density results in poortheological characteristics of highly loaded suspensions of tungstenpowder in a molten polymer. Consequently, shape forming with thesemixtures is not straightforward. Thus, the maximum density obtainable bythese mixtures is typically below about 11 g/cc.

[0015] U.S. Pat. No. 6,045,601 describes the use of a mixture oftungsten, stainless steel and an organic binder in a process to preparea sintered final article that is devoid of the organic binder. Themixture of tungsten, stainless steel and an organic binder is notintended as a final article and does not possess the desired impactcharacteristics since it is made with a large wax component that isbrittle in nature.

[0016] U.S. Pat. No. 5,616,642 describes lead-free frangible ammunitionmade from a metal powder, a polyester and a small amount of ionomer. Thecomposites described in this patent do not possess a combination of highdensity, suitable processing characteristics and malleability.

[0017] U.S. Pat. No. 6,048,379 describes a composite material comprisingtungsten, fibre and binder. There is no teaching of the compositematerials comprising tungsten powder with another metal powder having ahigh packing density.

[0018] There still remains a need for a tungsten/polymer compositematerial having a suitably high density, suitable processingcharacteristics and suitable malleability.

SUMMARY OF THE INVENTION

[0019] The present invention provides an article of manufacturecomprising a composite comprising: (a) tungsten powder; (b) anothermetal powder having a high packing density; and, (c) an organic binder.

[0020] There is also provided a composite comprising: (a) tungstenpowder; (b) another metal powder having a high packing density; and, (c)an organic binder.

[0021] Further provided is a process for producing an article ofmanufacture, the process comprising:

[0022] (a) mixing tungsten powder and another metal powder having a highpacking density to form a powder mix;

[0023] (b) formulating the powder mix and organic binder into thecomposite; and

[0024] (c) forming the composite into the article of manufacture withoutsintering.

BRIEF DESCRIPTION OF THE DRAWINGS

[0025] The invention will now be described by way of non-limitingexample with reference to the following drawings:

[0026]FIG. 1 is an electron micrograph of as-received tungsten powderprior to rod milling;

[0027]FIG. 2 is an electron micrograph of tungsten powder after rodmilling;

[0028]FIG. 3 is a graph of mixing torque as a function of solids loadingfor milled and unmilled tungsten powder;

[0029]FIG. 4 is a graph of mixing torque as a function of solids loadingfor rod-milled tungsten powder;

[0030]FIG. 5 is a graph of mixing torque as a function of solids loadingof 17-4PH stainless steel powder;

[0031]FIG. 6 is a diagram of a process for forming composites of thepresent invention;

[0032]FIG. 7 is a diagram of a process for producing shot;

[0033]FIG. 8 is an electron micrograph of 17-4 PH stainless steelpowder;

[0034]FIG. 9 is an electron micrograph of milled tungsten powder;

[0035]FIG. 10 is an electron micrograph of the fracture surface of acomposite of the present invention;

[0036]FIG. 11 is an electron micrograph of an extrudate produced inaccordance with the present invention;

[0037]FIG. 12 is an electron micrograph of milled carbonyl iron powder;

[0038]FIG. 13 is a photograph of shot being produced by heading orroll-forming technique;

[0039]FIG. 14 is an electron micrograph of the microstructure of shotformed according to the present invention;

[0040]FIG. 15 is an electron micrograph of bronze powder; and,

[0041]FIG. 16 is a picture of shot produced in accordance with thepresent invention.

DESCRIPTION OF PREFERRED EMBODIMENTS

[0042] Composites:

[0043] Tungsten is used in the composite preferably in an amount ofabout 80-99%, or about 80-97%, or about 80-96%, or about 87-93%, byweight of the composite. Tungsten is used in the form of tungsten powderthat is usually polygonal in shape. The mean particle size is preferablyabout 0.5-50 μm, more preferably about 1-50 μm, more preferably still2-20 μm and more preferably still 1-10 μm.

[0044] The tungsten powder is preferably milled to deagglomerate thefine particle clusters that are usually present and to improve thepacking density. This is illustrated by FIGS. 1 and 2. Deagglomeratingthe tungsten powder by rod-milling results in a lower and more uniformmelt viscosity of the tungsten/other metal powder/binder mix. This isevident from the variations in the mixing torque of the composite duringmelt processing for various as-received and processed tungsten powders.FIG. 3 shows mixing torque as a function of solids loading for milledand unmilled tungsten powder. FIG. 4 shows mixing torque as a functionof solids loading for rod-milled tungsten powder. In both FIGS. 3 and 4,the binder phase used was a paraffin wax-polypropylene-stearic acidblend and the melt temperature was 170° C. The results of FIG. 3 aretypical for commercial grades of tungsten powder. When the results ofthe rod-milled powder of FIG. 4 are compared to those of the milledpowder of FIG. 3, the maximum loading levels of FIG. 4 show a 7% gain inloading to reach 3 N-m.

[0045] The use of another metal in powder form, rather than in otherforms such as fibres, is believed to contribute to superior packing inthe composite resulting in higher achievable densities and superiorrheology in suspensions. Preferably, the other metal powder issubstantially or essentially spherical to further maximise packingdensity when mixed with the tungsten powder. The other metal can be anymetal that has a high packing density when blended with tungsten. Forrandomly packed spherical metal particles, a packing density of 62% byvolume or greater is considered high. For ordered packing of spherical(i.e. hexagonal close packing), a packing density of 72% by volume orgreater is considered high. For randomly packed spherical metalparticles of a metal powder having a wide or bimodal particle sizedistribution, a packing density of 72% by volume or greater isconsidered high. Preferably, the other metal is an austenitic orferritic stainless steel, iron, ferrous alloy, or bronze. Bronze is acopper/tin alloy typically having a Cu:Sn ratio of about 90:10, althoughother ratios of Cu:Sn may be possible. However, increasing theproportion of tin in the bronze may result in an increase in viscosityduring processing which makes processing more difficult. The other metalis preferably present in the composite in an amount of about 2-15%, orabout 3-15%, or about 7-12%, by weight of the composite. The meanparticle size is preferably about 1-50 μm, more preferably about 1-40μm, more preferably still about 5-25 μm and more preferably still about13-15 μm.

[0046] Like tungsten, the other metal powder can also be milled toprovide increased loading capacity. FIG. 5 shows mixing torque as afunction of solids loading of 17-4 PH stainless steel powder. The binderphase used was a paraffin wax-polypropylene-stearic acid blend. The melttemperature was 170° C. Loading levels shown are 10% higher than typicalunmilled powders commercially available.

[0047] The relative particle size of the metal powders as well as theirrelative proportions in the mixture are usually adjusted in order toobtain the desired combination of density and processibility. The meanparticle size of the other metal powder could be smaller than that ofthe tungsten so that the other metal powder particles will convenientlyfill the spaces between tungsten particles, which increases thecompaction of the composite resulting in a higher density.Alternatively, controlling the width of the particle size distributionwill enable the production of a mix of suitable packing density.

[0048] Organic binders are generally melt processible, have glasstransition temperatures well below room temperature, and provide goodimpact properties. The binder may comprise a single polymeric entity ora blend of different polymers. The organic binder may also be referredto as an organic matrix binder since it remains part of the finishedarticle after processing and becomes part of the matrix for holding thecomposite together. Since the final article in accordance with thepresent invention is not sintered, organic binder is not burned off andremains in the finished article.

[0049] The binder preferably comprises a relatively high viscosityrubbery phase provided by a thermoplastic elastomer (TPE) or a blend ofthermoplastic elastomers. Examples of thermoplastic elastomers include,but are not limited to, polyether block amides (e.g. Pebax™ grades fromAtofina), polyester elastomers (e.g. Hytrel™ grades from DuPont), meltprocessible rubber, chlorinated polyethylene (e.g. Tyrin™ grades fromDuPont Dow Elastomers), ethylene propylene diene monomer (EPDM) rubber(e.g. Nordel™ grades from DuPont Dow Elastomers), polyamide elastomers(e.g. Grilamid™ grades from EMS-Chemie), polyolefin elastomers (e.g.ethylene octene copolymer) and thermoplastic polyurethanes (TPU).

[0050] Other processing aides that may also be present in the binderinclude, but are not limited to, rheology or flow modifiers, strengthenhancing agents, surfactants (e.g. a wax and a fluoropolymer), andmixtures thereof. Some specific examples of other processing aides areethylene vinyl acetate, chemically modified polyethylene, zinc stearate,ethylene-bis-stearamide, stearic acid, paraffin wax and polyvinylidenefluoride. As used herein, the term “organic binder” refers to allorganic components in the composite.

[0051] The binder, including other processing aides, is preferablypresent in the composite in an amount of about 1-10%, or about 2-6%, byweight of the composite.

[0052] Packing density and overall density is achieved by the propertiesof the metal constituents. The organic binder essentially provides forthe ductility, toughness and malleability of the composite. Densitiesobtainable in the composite are preferably 10.5 g/cc or higher,especially from 11.0 g/cc to 12.0 g/cc. The composites are both strongand ductile and are softer than steel on the surface. Composites of thepresent invention are used unsintered in the final article ofmanufacture.

[0053] The composite preferably consists essentially of tungsten powder,another metal powder having a high packing density, and an organicbinder. However, the composite may include trace amounts of othermaterial as impurities, such as other metals (for instance nickel, zinc,bismuth, copper, tin and iron). Also, as one skilled in the art willappreciate, incidental impurities may be present, which do not undulyaffect the properties of the composite.

[0054] The characteristics of high density, shape preservation, strengthand malleability of the composite of the present invention is asignificant improvement over currently available composites,particularly for ballistic shot options. These characteristics make thecomposites of the present invention a good replacement for lead in avariety of finished articles.

[0055] Articles of Manufacture:

[0056] The unsintered composites of the present invention can be used ina variety of finished articles of manufacture, such as, for example,projectiles or ammunition (e.g., bullets, bullet cores and shot),weights (e.g., wheel balancing weights, such as clip-on balance weightsand adhesive balance weights), radiation shielding and high-densitygyroscopic ballasts. Preferably, the composite may be used inmanufacturing projectiles or ammunition, particularly shot, since thecomposite has an excellent combination of density, processibility andmalleability (deformation on impact), which is ideal for the manufactureof shot. In one method of making shot, semi-solid feedstock produced bymelt-processing a composite of the present invention may be charged intoan opening in a mould, through a channel and into mould cavities to formshot.

[0057] Processes:

[0058] A number of processes may be used to make the composites of thepresent invention and are generally disclosed in Manufacturing withMaterials, eds. Lyndon Edwards and Mark Endean, 1990,Butterworth-Heinemann, Oxford, UK; and, Process Selection: From Designto Manufacture, K. G. Swift and J. D. Booker, 1997, Arnold Publishers,London, UK, the disclosures of which are hereby incorporated byreference. These processes include Powder-Injection Moulding andextrusion.

[0059] The composites of the invention include an organic binder,generally a thermoplastic binder, in sufficient quantity to allow shapeforming methods to be used. Examples of this type of processing includePowder Injection Moulding (PIM). Powder injection molding (PIM) combinesthe processibility of plastics and the superior material properties ofmetals and ceramics to form high performance components. In recentyears, PIM has emerged as a method for fabricating precision parts inthe aerospace, automotive, microelectronics and biomedical industries.The important benefits afforded by PIM include near net-shape productionof complex geometries at low cost and rapid fabrication at highproduction volumes. When using metal powder feedstock, the process isusually referred to as Metal Injection Moulding (MIM).

[0060] The MIM process consists of several stages. Metal powders andorganic binder are combined to form a homogeneous mixture that isreferred to as the feedstock. Usually, the feedstock is a preciselyengineered system. The constituents of the feedstock are selected andtheir relative amounts are controlled in order to optimize theirperformance during the various stages of the process. Such controldepends on the particular constituents and is best left to the judgementof one skilled in the art during the process. Injection of the feedstockinto the mould is typically done at elevated temperatures (typicallybetween 100° C. to about 350° C.). The semi-solid feedstock is used tomould parts in an injection moulding machine, in a manner similar to theforming of conventional thermoplastics. Cooling the moulded semi-solidcomposite yields a solid article.

[0061] One skilled in the art will understand that PIM and MIMtechniques usually encompass a sintering step. Since the composites ofthe present invention are not sintered, PIM and MIM techniques appliedto this invention are best viewed as modified PIM and MIM processes.Modified PIM and MIM processes (i.e. without sintering) are suitableprocesses for mass production of finished articles like weights (e.g.wheel weights) and ammunition (e.g. bullet cores, shot).

[0062] Extrusion involves mixing the metal powders and organic binder atan elevated temperature (typically at about 100-350° C., more preferablyfrom about 250-285° C., still more preferably from about 250-270° C.,followed by extruding the mixture through an open die into the form ofwires, sheets or other simple shapes.

[0063] As an example, in this invention, tungsten and stainless steelpowders are mixed together with organic binder to form a suspension andextruded to form a wire, strip or sheet. In most extrusion equipmentthere is a defined zone built in for compounding prior to the extrudateexiting the die nozzle. The wire, strip or sheet may then be formed intothe desired article. For the production of shot, the wire, strip orsheet is stamped or rolled out to give substantially or essentiallyspherical composite particles. Press rolls may also be used to press theextruded composite into a desired thickness before the sphericalcomposite particles are formed. The spherical composite parts may thenbe finished to produce shot.

[0064] In a further example, tungsten and stainless steel powders may bepre-mixed to form an intimate-mixture of metals and charged to the firstport of an extruder followed by the addition of organic binder prior toextrusion; or, tungsten and the other metal powder may be pre-mixed withthe organic binder, then compounded and pelletized, and charged to anextruder. Pre-mixing is generally done at ambient (room) temperature.The extruded composite, in the form of a wire, strip or sheet, may thenbe stamped progressively using a series or an array of punches to formregular indentations until the spherical composite parts are finallystamped out. Alternatively, spinning rolls with a dimpled texture may beused to form spherical composite parts.

[0065] In another aspect, the other metal powder together with organicbinder may be charged to an extruder and tungsten introduced just priorto extrusion. The suspension to be extruded may be extruded cold, or,preferably, may be heated into a semi-solid state and maintained at anelevated temperature (typically at about 100° C. to about 350° C.). Thesemi-solid state comprises solid metal particles suspended in meltedorganic binder.

[0066] The residence time of the semi-solid suspension and the pressurein the compounder and/or extruder depend on the particular equipmentbeing used and on the desired properties of the resultant composite.Determination of residence time and pressure is well within the scope ofone skilled in the art to determine by simple experimentation.

[0067] It may be desirable to dry the metal powders before compoundingand to degas the metal/binder suspension during compounding in order toreduce back pressure. Too much back pressure can lead to poordensification, to lack of uniformity of the composite and to unwanteddensity variations in the finished article.

[0068]FIG. 6 is a diagram of an injection moulding and extrusionprocess, which is suitable for forming articles of the presentinvention. In FIG. 6, tungsten powder (130) is combined with anothermetal powder having a high packing density (140) to form a blend ofpowders to which an organic binder is added (150). The blend is thencharged into a compounder (160) for further mixing at an elevatedtemperature (e.g. 100-350° C.) and then extruded into a master batch ofpellets (170). The pellets (170) are then charged into an extruder(180), which carries the semi-solid feedstock into the mould (190).

[0069]FIG. 7 is a diagram of an extrusion process suitable for producingshot. Tungsten powder-other metal powder-organic binder blend (200) ischarged into a heated barrel (210) of an extruder (220). The blend (200)may be a simple blend or in a pelletized form as produced in FIG. 6. Themixture is heated in the barrel and forced through an extrusion nozzle(230) by an extrusion ram (240). The extrudate (245) is forced through adie plate (250) and extruded into a sheet, which is fed through twospinning rolls (260). The rolls have a dimpled surface to cut into thesheet and form shot (270).

[0070] Other techniques include tape casting, compaction, heading,roll-forming, and polymer-assisted extrusion. All of these approachesallow for the manufacture of net-shaped or near net-shaped green bodyhigh performance composite components by using the processibility ofpolymers with selected material property combinations of metals.

[0071] Tape casting usually involves mixing the metal powders andorganic binder and extruding the mixture at room temperature intosheets.

[0072] Heading or roll-forming techniques, either cold or warm, is morerapid than injection moulding and is ideally suited to the manufactureof ammunition, such as shot, since high throughput is required to makethe process more economical. Generally, the tungsten powder, the othermetal powder and the organic binder are mixed to form a suspension andextruded to form a wire, strip or sheet. Shot is produced when dimpleson the rolls of the apparatus cut into the extrudate thereby forming theshot.

[0073] In yet another technique, particularly adapted to producing shot,the ingredients of the composite including organic binder are mixedtogether, the organic binder is melted to form a suspension and themolten composite is dripped into small spheres.

[0074] All these processing techniques involve initial mixing of themetal ingredients with an organic binder to form a suspension of themetal particles in the organic binder. The organic binder contributesfluidity and modifies rheology of the composite mixture duringprocessing, thus permitting the forming of accurate dimensional shapes.

[0075] In some cases, the preceding processes may be followed by highenergy blending accomplished in a compounder. Typical compounders have abore with a single or double screw feed and a series of paddles forslicing and shearing the feedstock. Improved densification can beachieved by compounding. The compounded mixture is then shaped by usingone of a variety of forming techniques familiar to those skilled in theart.

[0076] All of these processing techniques can be used for the productionof composite products. Each technique would be chosen depending uponcomplexity of end product and volume of production. Forming processesare typically carried out at temperatures and pressures that arepredetermined by the rheology of the mixture of metal powders andorganic binder.

EXAMPLES

[0077] In order to identify suitable compositions of metal powder andorganic binder, calculations were performed using the inverse rule ofmixtures for a two-component mixture.$\frac{1}{\rho_{mixture}} = {\frac{1 - X}{\rho_{binder}} + \frac{X}{\rho_{powder}}}$

[0078] where:

[0079] X is the weight fraction of the metal powder in the composite

[0080] ρ_(mixture) is the density of the mixture

[0081] ρ_(binder) is the density of the organic binder

[0082] ρ_(powder) is the density of the metal powder

[0083] The equation can be extended for mixtures containing more thantwo constituents. For the examples which follow, the metal powder phaseconsisted of tungsten and one other metal powder selected from the groupconsisting of 17-4 PH stainless steel, 90Cu:10Sn bronze and carbonyliron. The solids loading of the metal powder mix was varied in the rangeof 55-65 vol %. The amount of tungsten in the mixture is represented asa weight fraction of the tungsten-metal powder mixture. The results ofthe calculations are presented below.

[0084] For each particular weight fraction of tungsten, the mix densityis given as a range. The lowest number of the range represents the mixdensity at a solids loading of 55 vol %. The highest number representsthe mix density at a solids loading of 65%. An incremental increase of 1vol % in the solids loading corresponds to a proportionate incrementalincrease in the mix density between the lowest and highest mix densitiesgiven for the particular weight fraction of tungsten. For example, themix density of tungsten/17-4 PH stainless steel at a tungsten weightfraction of 0.95 and a solids loading of 60 vol % is about 11 g/cc,which is the midpoint in the range of 10 to 12 g/cc given for a 0.95weight fraction of tungsten in the tungsten/stainless steel mix.

[0085] Tungsten/17-4 PH Stainless Steel: wt. fraction of W mix density(g/cc) 0.8 8.5 to 10  0.85    9 to 10.75 0.9  9.5 to 11.25 0.95 10 to 121.0 11 to 13

[0086] Tungsten/90Cu:10Sn Bronze: wt. fraction of W mix density (g/cc)0.8   9 to 10.5 0.85 9.25 to 11   0.9   10 to 11.75 0.95 10.25 to 12.251.0 11 to 13

[0087] Tungsten/Carbonyl iron: wt. fraction of W mix density (g/cc) 0.88.5 to 10  0.85    9 to 10.75 0.9  9.5 to 11.25 0.95 10 to 12 1.0 11 to13

[0088] It can be inferred from the data above that the densestcomposites (densities >11 g/cc) can typically be obtained at solidsloading >55 vol % and a tungsten fraction >95 wt % based on the weightof the composite.

[0089] In the following specific examples, the organic binder is a blendof several constituents:

[0090] a relatively high viscosity rubbery phase provided by athermoplastic elastomer (e.g., polyether block amides (Pebax™ gradesfrom Atofina), polyester elastomers (Hytrel™ grades from Dupont),ethylene propylene diene monomer rubber (Nordel™ grades from Dupont DowElastomers));

[0091] a rheology modifier for reducing the viscosity of the rubberyphase and provided by a low molecular weight polymer (e.g., ethylenevinyl acetate (Elvax™ grades from Dupont));

[0092] a strength enhancing agent provided by a chemically modifiedpolyethylene (e.g., Fusabond™ from Dupont); and/or,

[0093] a surfactant provided by a wax and a fluoroploymer (e.g.,ethylene-bis-stearamide (Acrawax™ C grade from Lonza), andpolyvinylidene fluoride (Kynar™ 2850 grade from Atofina)).

EXAMPLE 1 Tungsten-Stainless Steel-Polymer (1)

[0094] A mixture of 17-4 PH stainless steel powder and milled tungstenpowder was formulated with organic binders as shown in Table 1. Theformulation was achieved by mixing the ingredients in a Sigma™ blademixer at 220° C. and extruding the mixture out of a cylindrical die. Thedensity of the mixture was 11.03 g/cc. An electron micrograph of thefracture surface of the resulting composite is shown in FIG. 10. FIG. 8is an electron micrograph of 17-4PH stainless steel having the followingparticle size distribution: D₁₀=3.2 μm; D₅₀=6.9 μm; and D₉₀=11.8 μm.FIG. 9 is an electron micrograph of milled tungsten powder. The milledtungsten powder of FIG. 9 has an apparent density of 7.8 g/cc, a Tapdensity of 10.0 g/cc, a density determined by pycnometer of 19.173 g/ccand the following particle size distribution: D₁₀=5.65 μm; D₅₀=10.961μm; and D₉₀=18.5 μm. Composition of the stainless steel powder (17-4PH), from Osprey Metals Ltd, is shown in Table 1B. TABLE 1A Amount inFractional wt. of composite Density Metal Powders metal powder (% bywt.) (g/cc) Mass (g) 17-4 PH 0.1 9.67 7.621 16.0 stainless steeltungsten 0.9 87.06 19.2 144.01 Amount in Fractional wt. of compositeDensity Binder binder (% by wt.) (g/cc) Mass (g) Polypropylene 0.45 1.471 2.43 (proFlow ™) Ethylene vinyl 0.45 1.47 1 2.43 acetate Ethylene-bis-0.1 0.33 1 0.54 stearamide

[0095] TABLE 1B Composition of 17-4 PH Stainless Steel Cr Cu Ni Mn Si NbN Mo O C P S Fe 16.4 4.6 4.3 0.57 0.33 0.28 0.091 0.090 0.054 0.0370.018 0.003 Bal

EXAMPLE2 Tungsten-Stainless Steel-Polymer (2)

[0096] A mixture of 17-4 PH stainless steel powder, (FIG. 8), and milledtungsten powder (FIG. 9) was formulated with organic binder inproportions as in Table 2. Composition of the stainless steel powder(17-4PH), from Osprey Metals Ltd, is shown in Table 1B above.Formulation was achieved by initially mixing the ingredients in aReadco™ continuous compounder between 40-70° C. and injection mouldingthe compounded material at 230° C. with a mould temperature of 100° C.The injection speed was 200 ccm/s. The solids loading was 59 vol % andthe density of the formulation was 11.34 g/cc. TABLE 2 Amount inFractional wt. composite Density Metal Powders of powder (% by wt.)(g/cc) Mass (g) 17-4 PH stainless steel 0.025 2.41 7.75 819.34 tungsten0.975 93.90 19.2 31954.16 Amount in Fractional wt. composite DensityBinder of binder (% by wt.) (g/cc) Mass (g) Elvax ™ 450 0.05 0.18 0.9562.74 Pebax ™ 7233 0.88 3.25 1.02 1104.28 Acrawax ™ C 0.01 0.04 1.112.55 Kynar ™ 2850 0.01 0.04 1.75 12.55 Fusabond ™ 0.05 0.18 1.0 62.74MB 226D

EXAMPLE3 Tungsten-Stainless Steel-Polymer (3)

[0097] A mixture of 17-4 PH stainless steel powder, (FIG. 8), and milledtungsten powder (FIG. 9) was formulated with organic binder inproportions as shown in Table 3. Composition of the stainless steelpowder (17-4PH), from Osprey Metals Ltd, is shown in Table 1B.Formulation was achieved by initially mixing the ingredients in aReadco™ continuous compounder between 40-70° C. and injection mouldingthe compounded material at 230° C. with a mould temperature of 100° C.The injection speed was 200 ccm/s. The solids loading was 59 vol % andthe density of the formulation was 11.35 g/cc. The hardness (Hv) wasfound to be 23.1±1.5. Deformation characteristics (relativemalleability) of this product were analysed by a fully calibratedfalling weight test. (The falling weight test involved dropping a 847gram weight from a height of 33 mm above the upper surface of asubstantially spherical sample (3.5 mm nominal diameter) and measuring achange in thickness of the sample. The test can be viewed as a relativeimpact deformation measurement. A sample of a sphere made of thecomposite of the present invention was about 73% as thick after the testas before. In comparison, commercial lead shot was about 45% as thickand Tungsten Matrix™ shot (a tungsten/polymer shot from Kent Cartridge)was about 76% as thick. Thickness after impact was measured between theflat surfaces created by the impact. No fragmentation was observed inany of the materials, indicating malleability in all cases. The sampleof the present invention has a malleability comparable to prior arttungsten/polymer composites while having a superior density.Particularly noteworthy is the capacity to load tungsten in thecomposite of the present invention to higher than the 56 vol %. An SEMimage of the microstructure of the extrudate produced from theformulation in Example 3 is shown in FIG. 11. TABLE 3 Amount inFractional wt. composite Density Metal Powders of powder (% by wt.)(g/cc) Mass (g) 17-4 PH stainless 0.025 2.41 7.75 136.56 steel tungsten0.975 93.90 19.2 5325.69 Amount in Fractional wt. composite DensityBinder of binder (% by wt.) (g/cc) Mass (g) Elvax ™ 450 0.45 1.7 0.9596.58 Hytrel ™ 5526 0.38 1.44 1.2 81.56 Acrawax ™ C 0.01 0.04 1.1 2.15Kynar ™ 8250 0.01 0.04 1.75 2.15 Fusabond ™ 0.15 0.57 1.0 32.19 MB 226D

EXAMPLE4 Tungsten-Iron-Polymer (4)

[0098] A mixture of carbonyl iron powder, and milled tungsten powder(FIG. 9) was formulated with an organic binder in proportions as shownin Table 4. FIG. 12 is an electron micrograph of milled carbonyl ironpowder having an apparent density of 2.76 g/cc; a Tap density of 3.82g/cc; a density determined by pycnometer of 7.85 g/cc; and the followingparticle size distribution: D₁₀=1.98μm; D₅₀=4.541 μm; and D₉₀=13.41 μm.Carbonyl iron powder, from Reade Advanced Materials, is essentially pureiron with traces of oxygen and carbon. Formulation was achieved byinitially mixing the ingredients in a Readco™ continuous compounderbetween 40-70° C. and injection moulding the compounded material at 230°C. with a mould temperature of 100° C. The injection speed was 200ccm/s. The solids loading was 59 vol % and the density of theformulation was 11.35 g/cc. The formulation was found to haveTheological characteristics that confirmed that it was melt processible.The composite formed is strong and ductile and is softer on the surfacethan iron alone. TABLE 4 Amount in Fractional wt. composite DensityMetal Powders of powder (% by wt.) (g/cc) Mass (g) Carbonyl Iron 0.0252.41 7.8 819.65 Tungsten 0.975 93.91 19.2 31966.4 Amount in Fractionalwt. composite Density Binder of binder (% by wt.) (g/cc) Mass (g)Elvax ™ 450 0.05 0.18 0.95 62.74 Pebax ™ 7233 0.88 3.24 1.02 1104.28Acrawax ™ C 0.01 0.04 1.1 12.55 Kynar ™ 2850 0.01 0.04 1.75 12.55Fusabond ™ 0.05 0.18 1.0 62.74 MB 226D

EXAMPLE5 Bronze-Tungsten-Polymer (5)

[0099] A mixture of bronze powder, and milled tungsten powder (FIG. 9)was formulated with an organic binder in proportions as shown in Table5. FIG. 15 is an electron micrograph of bronze powder 300×magnification.Formulation was achieved by initially mixing the ingredients in aReadco™ continuous compounder between 40-70° C. and injection mouldingthe compounded material at 230° C. with a mould temperature of 100° C.The injection speed was 200 ccm/s. The solids loading was 59 vol % andthe density of the formulation was 11.43 g/cc. The formulation was foundto have rheological characteristics that confirmed that it was meltprocessible. The composite formed is strong and ductile and is softer onthe surface than bronze alone. Examples of shot that have been producedusing the formulation in Example 5 and using a compounding, extrusionand roll-heading operation are shown in FIG. 16. TABLE 5 Amount inFractional wt. composite Density Metal Powders of powder (% by wt.)(g/cc) Mass (g) Bronze 0.025 2.41 7.8 275.24 Tungsten 0.975 93.93 19.210734.23 Amount in Fractional wt. composite Density Binder of binder (%by wt.) (g/cc) Mass (g) Elvax ™ 450 0.05 0.18 0.95 20.91 Pebax ™ 72330.88 3.22 1.02 368.09 Acrawax ™ C 0.01 0.04 1.1 4.18 Kynar ™ 2850 0.010.04 1.75 4.18 Fusabond ™ MB 0.05 0.18 1.0 20.91 226D

EXAMPLE6 Tungsten-Stainless Steel-Polymer (6)

[0100] A mixture of 17-4 PH stainless steel powder, (FIG. 8), and milledtungsten powder (FIG. 9) was formulated with organic binder inproportions as in Table 6. Composition of the stainless steel powder(17-4PH), from Osprey Metals Ltd, is shown in Table 1B above.Formulation was achieved by pre-blending the ingredients in aparticulate form in a Readco™ twin-screw compounder. The temperaturesettings were 190° C., 200° C. and 210° C. in three zones between thefeeder and the die plate. The die plate was air cooled and maintained at150° C. The motor was running at 105 rpm and was drawing 3.5-3.7horsepower. The composite was granulated while exiting from thecompounder. The composite was passed through the compounder three timesbefore feeding into a Haake twin-screw extruder that had temperaturesettings of 60° C. at the feedstock inlet, 120° C. at the barrel, and100° C. at the die. The composite was fed through the extruder at 210cc/minute and the screw speed was 170 rpm. Cylindrical wires wereextruded in this manner through a 3 mm die for shot formation at a 4″drop to the rolls. The solids loading was 58 vol % and the density ofthe formulation was 11.12 g/cc. TABLE 6 Amount in Fractional wt.composite Density Metal Powders of powder (% by wt.) (g/cc) Mass (g)17-4 PH stainless 0.025 2.41 7.75 134.24 steel tungsten 0.975 94.13 19.25235.43 Amount in Fractional wt. composite Density Binder of binder (%by wt.) (g/cc) Mass (g) Elvax ™ 450 0.6 2.08 0.95 115.42 Nordel ™ IP4570 0.38 1.31 0.86 73.10 Acrawax ™ C 0.02 0.07 1.1 3.85

[0101] Examples of shot that have been produced using the formulationsin Examples 1-4 and using a compounding, extrusion and roll-headingoperation are shown in FIG. 13 with SEM image of the shot material shownin FIG. 14. Shot produced using a composite of Examples 1-4 exhibitsuperior ballistics properties. Shotgun patterns from a 12-gauge shotgunshow high pattern density and even spread with a growing pattern. Theshot is particularly useful for shooting bird game, such as pheasantsand partridge, at short range.

[0102] Other advantages which are inherent to the structure are obviousto one skilled in the art. It is apparent to one skilled in the art thatmany variations on the present invention can be made without departingfrom the scope or spirit of the invention claimed herein.

[0103] It will be understood that certain features and sub-combinationsare of utility and may be employed without reference to other featuresand sub-combinations. This is contemplated by and is within the scope ofthe claims.

[0104] Since many possible embodiments may be made of the inventionwithout departing from the scope thereof, it is to be understood thatall matter herein set forth or shown in the accompanying figures is tobe interpreted as illustrative and not in a limiting sense.

Having described the invention, what is claimed is:
 1. A compositecomprising tungsten powder, another metal powder having a high packingdensity and an organic binder.
 2. The composite according to claim 1,wherein the packing density of the other metal powder is 62 vol % orgreater.
 3. The composite according to claim 1, wherein the organicbinder comprises a thermoplastic elastomer or a blend thereof.
 4. Thecomposite according to claim 1, wherein the packing density of the othermetal powder is 62 vol % or greater, and wherein the organic bindercomprises a thermoplastic elastomer or a blend thereof.
 5. The compositeaccording to claim 4, wherein the organic binder comprises a polyetherblock amide, a polyester elastomer, a melt processible rubber, achlorinated polyethylene, an ethylene propylene diene monomer (EPDM)rubber, a polyamide elastomer, a polyolefin elastomer, a thermoplasticpolyurethane (TPU), or a blend thereof.
 6. The composite according toclaim 1, wherein the organic binder comprises a polyether block amide ora polyester elastomer.
 7. The composite according to claim 4, whereinthe organic binder comprises a polyether block amide or a polyesterelastomer.
 8. The composite according to claim 4, wherein the othermetal powder is stainless steel, iron, ferrous alloy or bronze.
 9. Thecomposite according to claim 4, wherein the other metal powder isbronze.
 10. The composite according to claim 4, wherein the other metalpowder is stainless steel.
 11. The composite according to claim 4,wherein the tungsten is present in the composite in an amount of from80-99% by weight of the composite.
 12. The composite according to claim4, wherein the tungsten is present in the composite in an amount of from80-97% by weight of the composite, the other metal powder is present inthe composite in an amount of from 2-15% by weight of the composite, andthe organic binder is present in the composite in an amount of fromabout 1-10% by weight of the composite.
 13. The composite according toclaim 1 consisting essentially of tungsten powder, another metal powderhaving a high packing density and an organic binder.
 14. The compositeaccording to claim 13, wherein the packing density of the other metalpowder is 62 vol % or greater.
 15. The composite according to claim 13,wherein the organic binder comprises a thermoplastic elastomer or ablend thereof.
 16. The composite according to claim 14, wherein theorganic binder comprises a polyether block amide, a polyester elastomer,a melt processible rubber, a chlorinated polyethylene, an ethylenepropylene diene monomer (EPDM) rubber, a polyamide elastomer, apolyolefin elastomer, a thermoplastic polyurethane (TPU), or a blendthereof.
 17. The composite according to claim 14, wherein the organicbinder comprises a polyether block amide or a polyester elastomer. 18.The composite according to claim 16, wherein the tungsten is present inthe composite in an amount of from 80-99% by weight.
 19. The compositeaccording to claim 16, wherein the tungsten is present in the compositein an amount of from 80-97% by weight of the composite, the other metalpowder is present in the composite in an amount of from 2-15% by weightof the composite, and the organic binder is present in the composite inan amount of from about 1-10% by weight of the composite.
 20. A finishedarticle of manufacture comprising an unsintered composite comprisingtungsten powder, another metal powder having a high packing density andan organic binder.
 21. The article according to claim 12, wherein thepacking density of the other metal powder is 62 vol % or greater. 22.The article according to claim 21, wherein the organic binder comprisesa thermoplastic elastomer.
 23. The article according to claim 21,wherein the organic binder comprises a polyether block amide or apolyester elastomer.
 24. The article according to claim 22, wherein theother metal powder is stainless steel, iron, ferrous alloy or bronze.25. The article according to claim 22, wherein the tungsten is presentin the composite in an amount of from 80-97% by weight of the composite,the other metal powder is present in the composite in an amount of from2-15% by weight of the composite, and the organic binder is present inthe composite in an amount of from about 1-10% by weight of thecomposite.
 26. The finished article according to claim 20, wherein theunsintered composite consists essentially of tungsten, another metalpowder having a high packing density and an organic binder.
 27. Thearticle according to claim 26, wherein the packing density of the othermetal powder is 62 vol % or greater.
 28. The article according to claim27, wherein the organic binder comprises a thermoplastic elastomer. 29.The article according to claim 27, wherein the organic binder comprisesa polyether block amide or a polyester elastomer.
 30. The articleaccording to claim 28, wherein the other metal powder is stainlesssteel, iron, ferrous alloy or bronze.
 31. The article according to claim28, wherein the tungsten is present in the composite in an amount offrom 80-97% by weight of the composite, the other metal powder ispresent in the composite in an amount of from 2-15% by weight of thecomposite, and the organic binder is present in the composite in anamount of from about 1-10% by weight of the composite.
 32. The articleaccording to claim 22 which is ammunition, a weight, radiation shieldingor a high-density gyroscopic ballast.
 33. The article according to claim25 which is shot or a bullet core.
 34. The article according to claim 28which is ammunition, a weight, radiation shielding or a high-densitygyroscopic ballast.
 35. The article according to claim 31 which is shotor a bullet core.